1. Field of the Invention
This invention relates to hydraulically expanding tubes in a tubesheet of a heat exchanger and more particularly, to such a mandrel with an eddy current probe for detecting the inner edge of the tubesheet and such mandrel with a flexible central portion so that the mandrel may be inserted into a tube adjacent a hemispherical head.
2. Description of the Prior Art
A hydraulic tube expander mandrel having a ramp on which an O-ring seal rides was described in an application filed by the assignee June 28, 1977 and assigned Ser. No. 810,817, now U.S. Pat. No. 4,125,937.
U.S. Pat. Nos. 3,977,068 and 3,979,810 describe a simple mandrel and method for hydraulically expanding tubes into engagement with a tubesheet. The use of such mandrel as described therein are not satisfactory as the O-ring seals have a very short life.
When expanding a tube hydraulically, the portion of the tube expanded must be within the tubesheet as the pressurized fluid utilized causes the tube to yield and if the tube is not backed up by the tubesheet, it will burst. When hydraulically expanding a tube in a very thick tubesheet clad with a non-corrosive material on at least one side, the thickness of the tubesheet varies so that obtaining expansion generally throughout the portion in which the tube and tubesheet are contiguous requires very accurate positioning of the mandrel. Since one of the reasons for full-length expansion of a tube in a tubesheet is to eliminate crevice corrosion adjacent the inner edge of the tubesheet, accurate positioning of the leading end of the mandrel is critical. Utilizing a stop on the trailing end of the mandrel does not provide sufficiently accurate positioning of the leading end of the hydraulic expander relative to the inner edge of the tubesheet.